The non-uniform implantation of impurities in a semiconductor substrate has been employed to form buried channel charge transfer devices. The present invention utilizes a non-monotonic doping of donor type impurity ions in a semiconductor to produce a buried conduction channel in the semiconductor. Between the conductive channel and the surface of the semiconductor there is a region implanted with acceptor ions to serve as a charge storage region. According to preferred embodiments of the invention this region is conductively isolated from the remainder of the semiconductor body by the buried conductive channel and portions of an insulating region on the substrate. A gate electrode is positioned at the surface of the semiconductor and separated from the semiconductor by the insulating layer.
In operation, an electrical potential of appropriate magnitude and sign is applied to the gate electrode to deplete the buried conduction channel and thereby render the channel non-conductive. At this point in the operating cycle, majority carriers may begin to accumulate in the isolated charge storage region at the surface of the semiconductor. This charge may result from thermal or optical generation in the storage region, or from charge injection into the region. As increasing amounts of charge accumulate, an electric field is generated which tends to cancel the electrical field imposed by the gate electrode; the buried conduction channel is thereby restored to a conductive mode. By monitoring the conduction of the buried channel, it is possible to detect accumulated charge in the storage region. Thus, for example, if charge accumulates as a result of optical generation, the device may function as a transistor photodetector. If charge is injected into the charge storage region, the device may function as a memory.